, 
vl PREFACE. 
To endeavour, therefore, to expedite the completion of the work, it is 
proposed in future to treat each species, wherever possible, much more 
succinetly than heretofore, more especially in regard to the lists of fully 
detailed localities, as the time necessarily consumed in the compilation, 
comparison, and co-ordination of the enormous numbers of registered 
vecurrences of the various species 1s very great, and considerable time and 
space will be saved by these details being more briefly summarized. 
It is further very gratifying to find that the truth of the principles 
governing the Distribution of Life propounded in the present work, and 
firmly based on organic structure, continues to be increasingly supported 
by the additional knowledge acquired; while the especial suitability of 
the land mollusca for revealing the routes of dispersal from the primary 
evolutionary area was emphatically proclaimed by the late Karl Semper, 
who after many years’ examination and study of many hundreds of species 
was led more and more strongly to the conviction that a knowledge of 
the affinities of the land mollusca would probably enable the paths of 
their dispersion to be determined. 
The co-operation and help which I have received in the past from so 
many well-wishers has been continued during the preparation of the 
present volume, and I again recall with grateful appreciation the immense 
help I still continue to derive from the results of the unwearied and un- 
selfish labours of the late Mr. CHarLEs AsHrorD, who for so long a period 
devoted himself to a study of the anatomy of our British mollusks for the 
benefit of the present work. 
Mr. W. Dentson Rogsuck has continued in numberless ways his valued 
and helpful assistance, but more especially in the oversight of the innumer- 
able details involved in the allocation of the multitudinous localities to 
their correct comital or vice-comital districts, for which his official position 
as Hon. Recorder to the Conchological Society is a special qualification. 
Mr. W. Bacsuaw, of Birkenshaw, has rendered me great service by his 
excellent micro-photographs of the teeth, jaws, and other minute details 
of the structure of the shells and their animal inhabitants. 
The Rev. Pror. H. M. Gwarkin has given invaluable assistance by 
specially preparing the mandibles of any desired species, and also by 
granting me the privilege of the use of his unrivalled collection of radule. 
Mr. J. Davy Dean has also given me much appreciated help by his 
exquisite coloured drawings of living //yaliniw, and by his expert advice 
on the better representation of the shells of other groups. 
